Allow debugging of unit tests via wfDebugLog.

This adds a listener to the PHPUnit test runner that will report
testing progress via wfDebugLog. This is useful for debugging
situations in which phpunit itself fails to report errors and
does not terminate normally. Having a debug log should at least
help with locating the trigger of the problem.

Change-Id: I433537a7f26197d8cff6f133e26ae5709871500f
Merge "Allow debugging of unit tests via wfDebugLog."